The present invention is directed to a printing unit The printing unit has at least four cylinders that form two pairs. Transfer cylinders of the two pairs cooperate in a print-on position.
A four-cylinder printing unit is known from DE 196 03 663 A1. Two transfer cylinders which cooperate with each other are fixedly coupled to each other and can be selectively driven by the drive mechanism of one or of both associated forme cylinders, or via a transverse shaft which can be connected to the motors. In one mode of operation, one of the forme cylinders can be stopped for a plate change, while the associated transfer cylinder continues to run synchronously with the second forme cylinder.
EP 0 997 273 A2 discloses a mode of operation of a four-cylinder printing unit a forme cylinder is moved away from the remaining cooperating cylinders. In one example, the moved-away forme cylinder can be rotated by a drive motor, and in another example it can be rotated by an auxiliary motor.
A printing unit with two pairs of cylinders is known from EP 0 621 133 A1. Each of the cylinders of at least one pair has its own drive motor, which is independent of the remaining cylinders.
In accordance with the article xe2x80x9cDigitaler Direktantrieb an Druckmaschinenxe2x80x9d [Direct Digital Drive for Printing Presses], in Druckspiegel September 1999, cylinders and rollers can be separately controlled, for example in the course of independent change of several printing plates or while changing a rubber blanket, wherein the remaining units are stopped. It is also possible to operate each printing location, or printing group, independently of the others.
The object of the present invention is directed to providing a printing unit.
In accordance with the present invention, this object is attained by providing a printing unit with at least four cylinders that include a first pair with a first forme cylinder and a first transfer cylinder, as well as a second pair with a second forme cylinder and a second transfer cylinder. The two transfer cylinders cooperate in a print-on position. At least one of the transfer cylinders has a set-up rotational speed which differs from a production rotational speed and from zero. The associated forme cylinder also has a set-up rotational speed which differs from the production rotational speed and from a zero rotational speed.
The advantages which can be obtained by the present invention reside, in particular, in that a large operational diversity and variability of a printing unit or a cylinder assembly is created.
For example, it is possible in this way to move cylinders or groups of cylinders independently of each other at different rotational speeds, or also in different directions of revolutions, which may be required, for example, for a printing forme or for a rubber blanket change, when drawing in a paper web, or in the course of independent inking or washing of rollers and cylinders. In particular, different actions when setting up at set-up rotational speeds, or speeds different from the stop or zero rotational speed, or the production rotational speed for the individual cylinder types are therefore possible next to each other and with a paper web either running or stopped.
The simultaneous meeting of several different demands made on different components of a printing group or a printing unit is particularly advantageous by use of the printing unit in accordance with the present invention. For one, the operational modes contribute to time savings and therefore to a lowering of the production costs, and furthermore make possible the performance of various set-up operations at production speed or at draw-in speed of the running paper web. A flying plate change for single- or doubled-sided imprint operations is possible. For example, in advantageous operational states, a printing forme is changed or pre-inked, while the associated transfer cylinder continues to rotate at production speed. Washing, pre-inking or also a change of the dressing can take place.
An advantageous mode of operation of the printing unit, in the case of two pairs, each having a forme and a transfer cylinder, is the rotation of one of the forme cylinders at a setup rotational speed, while the remaining cylinders continue to rotate at production rotational speeds. Also, both transfer cylinders can be stopped or can rotate at a rotational speed for drawing in a paper web, or at production rotational speed while one of the forme cylinders, or both, are inked.
Variable operational modes are also provided, in an advantageous manner for four-cylinder printing units, and in particular for eight-cylinder printing units which are constituted by two four-cylinder printing units, in particular in respect to a flying plate change, or to an imprinter functionality. For example, the printing operation can be maintained, while one or several forme cylinders, whose rotational speed and also direction of rotation in part is different from the production rotational speed, are changed.
For example, a Y- or a lambda-shaped six-cylinder printing unit can be flexibly employed for a 2/1 print run, or also for a flying plate change, or for a imprint function during 1/1 printing, if one of the forme cylinders is operated at a rotation speed and in a direction of rotation for the change, while all of the remaining cylinders rotate at a production rotational speed. The transfer cylinder assigned to the forme cylinder to be changed is, for example, operated at the same time at a rotational speed and in a direction of rotation for washing, or for other set-up functions. This correspondingly also applies to a seven-, nine- or ten-cylinder printing unit.
For reasons of flexibility and of savings of time, as well as of waste, the operational states provided by the printing unit of the present invention are of great importance in the course of fitting prior to start-up, or at the end of the printing operation. For example, the forme cylinder and the transfer cylinder can simultaneously pass through different set-up programs.
The independent operation of the rollers for ink application, which are assigned to the forme cylinders, is also advantageous. For example, washing or pre-inking can take place regardless of the rotational speed and the direction of rotation of the forme cylinder and while the forme cylinder also passes through a set-up program.